I'm not aware of any resource in Planet Nomads named 'coal' -- I suspect, you're referring to 'Carbon'.
While I see the potential usefulness of being able to convert resources, the conversion you're suggesing doesn't appear to me as being particularly useful:
- You can simply drop what you don't need
- If a Biome has a great lot of Biomass, then either it also has a lot of Carbon, or is close to another Biome with lots of Carbon
- 15 Minutes for getting a single unit of Carbon is a lot of time. Depending on the properties of the planet, that's probably about the time you'd need to simply drive / hover / fly or even swim or walk to a Biome with lots of Carbon
Lastly, with a little bit of moving around, a Mining Machine can extract allmost all types of resources anywhere, at the very least the most commonly needed ones (albeit in miniscule amounts). And it allows for selecting, which resource it should mine.
A more useful conversion to me would be turning some resources into Biomass -- think of a self-sufficient polar base, for example.